Many devices and systems include various numbers and types of sensors. The varied number and types of sensors are used to perform various monitoring and/or control functions. Advancements in micromachining and other microfabrication techniques have enabled manufacture of a wide variety of microelectromechanical (MEM) devices, including various types of sensors. Thus, in recent years, many of the sensors that are used to perform monitoring and/or control functions are implemented using MEM sensors.
One particular type of MEM sensor that is used in various applications is a gyroscope. A MEM gyroscope is used to measure an angular rate of an object and may be constructed from a silicon-on-insulator wafer that includes a substrate layer, a sacrificial layer overlying the substrate layer, and an active layer overlying the sacrificial layer. Trenches are etched into the active layer and, in some cases, undercut the active layer, to form among other component parts, a proof mass and capacitive elements. The proof mass is resiliently suspended by one or more suspension springs and capable of moving along one or more of at least three orthogonal axes when the MEM gyroscope experiences a directional or speed change. The capacitive elements sense displacement of the proof mass, and the displacement is converted into an electrical signal having a parameter magnitude relating to angular rate.
Typically, the trenches that make up the proof mass and capacitive elements have substantially equal widths; however, some MEM devices, such as high aspect ratio MEM gyroscopes, may need trenches that do not have equal widths. For example, in instances in which a strong electrical signal is preferred, the capacitive elements may preferably be separated from one another by a narrow trench. If a MEM gyroscope having heightened sensitivity is preferred, a wide trench may be needed to surround the proof mass because the sensitivity depends on the amplitude of the oscillation of the proof mass.
In a conventional process for forming narrow and wide trenches on the same substrate, photoresist is first deposited over the substrate active layer in a predetermined pattern. The pattern includes component sections that are separated from one another by narrow and wide gaps. After the photoresist is deposited, material not protected by the photoresist is etched away. As a result, narrow and wide trenches are formed in the substrate.
However, because the material is etched away at a rate that is dependent on the width of the trench, more material is removed from the wide trench than from the narrow trench. Additionally, when the wide trench is completely etched down as desired, the narrow trench may not be completely etched. Thus, if both trenches are etched for a comparable amount of time, e.g. until the narrow trench is completely etched, the etchants may etch more of the wide trench than desired which may compromise the quality of the resulting MEM device. Moreover, the shape and profile of the wide trench may be affected by the increased time needed for completion of narrow trench etching. Consequently, the behavior and performance of the MEM device may be compromised.
In addition to incorporating trenches into the MEM device, interconnects may be needed to electrically connect different parts of the device. The interconnects form bridges and require a planar surface for proper formation. However, current etching technology does not provide for techniques for refilling trenches while also enabling the formation of the electrical interconnects.
Hence, it would be desirable to have a method of making a MEM device, that addresses one or more of the above-noted drawbacks. Specifically, it would be desirable to have a method in which both wide and narrow trenches having substantially equal depths may be formed in the same wafer. Moreover, it would be desirable to have a method that is relatively simple and inexpensive to implement. The present invention addresses one or more of these needs. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.